The subject invention relates to a ring seal assembly for reducing leakage about a part while permitting the part to radially expand under varying thermal conditions. More particularly, a ring seal assembly is disclosed for use with a part such as a shaft or piston cylinder, having a circular cross section. The assembly includes primary and secondary seal rings which are bonded together to substantially reduce leakage in both the axial and radial directions.
In the prior art, various sealing ring assemblies have been developed for use with moving parts to inhibit the leakage of fluids therearound. For example, ring seals have been developed which are mounted about rotating power shafts to prevent the leakage of lubricating fluids outwardly along the cylindrical surface of the shaft. Similarly, seal assemblies have been developed which are mounted about a piston for forming a sealing engagement with the wall of the piston cylinder.
Solid ring seals having radially inner and outer peripheral surfaces have been employed in simple low power devices. However, it is recognized that in the majority of high power engine applications, temperatures are generated which require ring seal assemblies that can accommodate the thermal expansion of the parts. More specifically, a solid sealing ring which was machined to conform to the dimensions of a cold shaft would shatter as the shaft expanded. Conversely, a solid ring machined to conform to the dimensions of an expanded shaft would not provide adequate sealing during the initial start-up stage of the engine.
A common ring seal assembly which has been developed to accommodate the thermal expansion of a part includes a seal ring having a radially extending gap or split. The split seal ring is provided with a radially inner diameter substantially conforming to the diameter of the cold shaft. As the temperature of the engine rises and the rotating shaft expands, the radially extending gap provided in the split ring permits the ring to expand along with the shaft. Preferably, a biasing means such as a garter spring is provided around the outer peripheral surface of the split ring to urge the inner surface thereof into sealing engagement with the rotating shaft.
Typically, a split ring is operative to eliminate approximately 98% of leakage about a rotating shaft. However, as can be appreciated, the radially extending gap in the ring does allow a small amount of axial leakage. In most high performance engine applications, leakage must be substantially eliminated. Accordingly, various expedients have been developed which are used in conjunction with a split ring in an effort to eliminate any leakage associated therewith. One example of such a ring seal assembly is disclosed in U.S. Pat. No. 3,430,967, issued Mar. 4, 1969 and assigned to the same assignee as the subject invention. In the assembly disclosed in the latter patent, a primary split ring is provided having an inner diameter substantially conforming to the diameter of the cold shaft. In addition, a solid secondary seal ring is provided wherein the radially inner peripheral surface includes a first portion or dam having a curvature substantially conforming to the curvature of the primary seal ring. The remaining portion of the radially inner surface of the secondary seal ring is undercut to allow for the thermal expansion of the shaft. In use, the primary and secondary rings are non-rotationally mounted in a seal case about a rotating shaft. The primary and secondary rings are disposed in face-to-face contacting relationship with the dam of the secondary ring being aligned directly behind the gap in the primary split ring. By this arrangement, the dam portion of the secondary ring functions to seal any axial leakage permitted by the gap in the split ring.
The sealing assembly disclosed in U.S. Pat. No. 3,430,967 is highly effective in eliminating leakage when the primary and secondary sealing rings are accurately machined. However, it was found that the overall effectiveness of mass produced seals is dependent upon the accuracy and talent of the machinist. More specifically, if the radially inner surfaces of the rings and particularly the dam portion of the secondary seal were not machined to the exact size of the shaft, some axial leakage would result. In order to minimize this effect, the secondary ring is provided with a dam which extends about 120.degree. of its circumference. As the angular extent of the arc of the dam is increased, any machining errors in the curvature may result in the shaft resting on the opposed end points of the dam, creating a gap which permitted the escape of fluids. On the other hand, if the angular extent of the arc of the dam is reduced, the ring seals tend to wobble about the shaft also permitting leakage. Accordingly, by providing a dam having 120.degree. arc extension, both problems are substantially minimized. However, even when the secondary ring is provided with 120.degree. dam, the total effectiveness of the seals are still dependent upon the skill of the machinist.
Accordingly, it is an object of the subject invention to provide a new and improved ring seal assembly which substantially eliminates leakage, while significantly simplifying the manufacture thereof.
It is another object of the subject invention to provide a new and improved ring seal assembly which substantially reduces leakage, while permitting the parts to radially expand under varying thermal conditions.
It is a further object of the subject invention to provide a new and improved ring seal assembly for reducing the leakage about a part such as a shaft or a piston cylinder having a surface of circular cross section.
It is still another object of the subject invention to provide a new and improved ring seal assembly which includes a primary split seal ring and a solid secondary seal ring, the latter being disposed in aligned, face-to-face relationship with the primary ring and bonded thereto at a point adjacent one side of the gap in the split ring. By this arrangement, leakage is substantially eliminated while machining of the ring seal assembly is significantly simplified. Further, the bonding of the rings tends to equalize the radial pressure on the elements resulting in a corresponding equalization of wear thereby increasing the life of the assembly.